1. Field of the Invention
The present invention relates to an optical fiber probe using an electrical potential difference and an optical recording and/or reproducing apparatus using the same, and more particularly, to an optical fiber probe using an electrical potential difference generated between a plurality of thin metal layers coated on the optical fiber probe and spaced-apart from each other to improve a light transmission rate, and an optical recording and/or reproducing apparatus using the same.
2. Description of the Related Art
Generally, in order to store more information in a unit area in an optical medium in an information recording apparatus, a wavelength of a laser beam emitted from a recording optical source should be reduced, and a numeral aperture of a condensing lens should be increased. The wavelength of the laser beam of the recording optical source can be reduced, and the numeral aperture of the condensing lens can be increased up to 1.0 using a blue laser diode. However, in a case of an optical information recording method, it is a limitation in storing the high density of information in a next generation optical information storing apparatus, which requires high dense recording, due to diffraction of light.
In order to overcome the above problems, there have been developed conventional technologies, such as a scanning probe recording (SPR) technology using a probe of an atomic force microscope, an ultra resolution medium technology, or a technology using a near-field optical fiber probe, to overcome the problems occurring due to the diffraction of the light.
As a first example of the conventional technologies, a technology is used for the near-field optical fiber probe to output the laser beam through a very small aperture having a diameter of tens nm or hundreds nm. However, the near-field optical fiber probe is mechanically weak and fragile, and a plurality of optical fiber probes cannot be accurately arranged. A light throughput (transmission) rate of the light passing through an opening of a near field optical probe is very small, for example, the light throughput rate is 10−5 through 10−7 in a case of the opening of 100 nm in size. Therefore, it is very difficult to utilize the near-field optical fiber probe technology in the optical information storage apparatus since a recording and data processing speed is very low. That is, in order to be used in the optical information recording apparatus, the near-field optical fiber probe technology requires the opening having a higher light throughput rate, and the near-field optical fiber probe is required not to be abrasive. Since it is very difficult to accurately arrange a plurality of near-field optical fiber probes, the conventional near-field optical fiber probes cannot be improved to meet a recording and reproducing speed required in the optical information recording and reproducing apparatus.
A technology of manufacturing a conventional probe unit having a plurality of openings using a semiconductor process as a second example of the conventional technologies will be explained in reference with FIG. 1.
Referring to FIG. 1, the probe unit includes a plurality of holders 11, a plurality of probes 12 disposed below corresponding ones of the holders 11, and a plurality of openings 13 formed between the adjacent probes 12. Since a light throughput (transmission) rate of a laser beam (light) passing through the openings 13 is lower than 10−5 like as the conventional optical fiber probe, the light throughput rate needs to be improved. A method of exciting Plasmon or another method of reducing an area in which an optical loss occurs from a wavelength of the end portion of the probes 12 has been used to improve the light throughput rate of the laser beam passing through the openings 13 formed on end portions of the probes 12.
As a third example, in the method of exciting the Plasmon to improve the light throughput rate of the laser beam passing through the openings 13 formed on the end portions of the probes 12, a Plasmon mode cannot effectively excite the Plasmon since an excitation efficiency depends on polarization of an incident beam. In order to effectively excite the Plasmon, a specific structure to excite the Plasmon should be formed using a particular process.
A fourth example of the conventional methods has been introduced to improve a structure of end portions of optical fiber probes by manufacturing openings having a higher light throughput rate of a laser beam so that an optical loss area is minimized. The conventional method of manufacturing the openings to reduce the optical loss area has been used to form the conventional optical fiber probes. The method includes forming a structure of the end portions of the optical fiber probes having a wide cone angle to form the openings, forming a reflective layer on a first taper area to reflect an incident beam, forming the reflective layer on the second taper area to widen the wide cone angle to reduce the optical loss area to a maximum degree, and forming a small opening of a probe shape in a third taper area to have the higher light throughput rate. However, in the method of forming the opening, a size of the opening having the maximum light throughput rate is determined according to a size of the first taper area, and the opening is formed through a plurality of wet-etching processes. Therefore, the method of forming the opening becomes complicated, and the probes formed by this probe method cannot be used in storing a high density of optical information since the end portions of the optical fiber probes are too bulky in size.
As a fifth example, the conventional method of forming the opening having the higher light throughput rate using the semiconductor process and the wet-etching process includes forming the probe using silicon etching processes including a non-uniform directional etching process, forming an oxide layer at a low temperature, and forming the end portion of the probe in a structure having an edge angle of a large parabola to reduce the optical loss area. However, in this large parabolic structure, the probe manufacturing process including the low temperature oxide layer forming process becomes complicated, and it is difficult to form the end portion of the probe in the large parabolic structure.
As described above, the light throughput rate may be improved by the conventional method of forming the opening. In addition, another conventional method including a silicon semiconductor manufacturing process similar to the above method of forming the opening by the reflective layer of the large cone angle structure has been proposed. FIG. 2 is a view showing another conventional near-field optical head manufactured using the silicon semiconductor manufacturing process.
Referring to FIG. 2, the conventional method includes forming a relatively large opening of 11 mm to 2 mm using the silicon semiconductor process, and coating a reflective layer thereon. This structure corresponds to the first taper area described in the fourth example of the conventional methods. A relatively small opening of 60 nm is formed on a center portion of the coated reflective layer so that the opening having the high light throughput rate is formed. A third non-linear thin layer is additionally coated on the reflective layer, and a self focusing, which is a characteristic of the third non-linear thin layer, is generated through the third non-linear thin layer to improve the light transmission (throughput) rate of the opening.
Although the conventional method of improving the light throughput rate may be used in forming the reflective layer within the first taper area and forming the opening on the reflective layer to form the opening having the high light throughput rate, it is difficult to physically implement this conventional method in forming the opening since the light mode reflected from the reflective layer cannot be completely transferred to all modes, which exist in the opening, using the reflective layer only. Moreover, in this conventional method of improving the light throughput rate, there still exists a large area, in which the light loss occurs like as the conventional optical fiber probe, in the opening. Furthermore, even if an additional thin coating layer is formed on the reflective layer to cause the self focusing, a self focusing phenomenon does not occur since reflective indexes are spatially different according to the nonlinear characteristic, and the reflective index determined in the previously formed structure is changed to another reflective index which is spatially different from the reflective index. Since the reflective index is changed, the change in the reflective indexes causes a phase difference in the laser beam, thereby distorting a beam size and a beam shape. The beam size may be enlarged since a defocusing phenomenon can occur rather than the self focusing. That is, in the coated structure formed with non-linear thin layer according to the above conventional method of improving the light throughput rate, reducing of the beam size is limited up to one wavelength of the light. The light throughput rate cannot be improved. Since the probe has a flat structure of the end portion rather than the probe structure, this structure cannot be used in storing the optical information, and it is impossible to implement a probe method and a near-field method.
In order to solve the above problems, Korean patent application No. 2001-74731 discloses a technology of generating a self focusing phenomenon, completely filling the opening with a material having a third non-leaner coefficient, reducing the beam size into a half of the wavelength of the laser beam, and focusing the laser beam in a parabolic shape having no optical loss to effectively excite the near-field in the opening disposed on the end portion of the probe, thereby increasing the light throughput rate of the optical information probe.
The technology disclosed in the Korean patent application No. 2001-74731 and improving the light (laser beam) transmission (throughput) rate will be explained in detail hereinafter.
FIG. 3 is a perspective view showing a structure of a conventional optical recording and/or reproducing head using a conventional laser beam transmission improving method disclosed in the Korean patent application No. 2001-74731. Referring to FIG. 3, the conventional optical recording and/or reproducing head includes two units.
The conventional optical recording and/or reproducing head include a lower structure and an upper structure. The lower structure is formed with a silicon substrate 21 as a head holder. The upper structure includes an opening 25 having a reverse trapezoidal shape filled with a non-linear material 28, and a metal thin layer 27 to form a probe, and an end portion of the upper structure is connected to the lower structure.
Here, the upper structure includes a silicon deposition layer 23, and a silicon oxide 22 is formed on a boundary of the upper structure and the lower structure. A plurality of probes formed with the metal thin layer 27 is formed on a lower portion of the upper structure. A portion of the non-linear material 28 filled in the opening 25 having the reverse trapezoidal shape formed on the silicon deposition layer 23 by an etching process is exposed through a lower portion of the silicon deposition layer 23 of the upper structure.
A method of manufacturing the optical recording and/or reproducing head having the above structure will be described hereinafter.
After the silicon oxide layer 22 is formed on a silicon substrate 21, the silicon deposition layer 23 is formed on the silicon oxide layer 22. After first and second nitride layers (not shown) are formed on an upper surface of the silicon deposition layer 23, a predetermined area of a lower portion of the silicon substrate 21 is exposed by patterning the first nitride layer formed on the lower portion of the silicon substrate 21. The exposed area of the silicon substrate 21 is 1 through 10 nm2. Here, a silicon oxide layer or a silicon nitride layer can be used as the first or second nitride layer.
In a state that the predetermined area of the lower portion of the silicon substrate 21 is exposed, the exposed predetermined area of the lower portion of the silicon substrate 21 is etched by a first etching process. The lower portion of the silicon substrate is etched by 1000 μm.
The first etching process is a wet-etching process to maintain the silicon substrate 21 by a predetermined thickness from the silicon oxide layer 22. Since the silicon deposition layer 23 is formed to be thinner than a thickness of the silicon substrate 21, the silicon deposition layer 23 is physically protected.
After the first etching process is finished, a predetermined area of the silicon deposition layer 23 is exposed by patterning the second nitride layer formed on the upper surface of the silicon deposition layer 23, and then a plurality of apertures 25 are formed by a second etching process.
Here, the second etching process is a dry-etching process. The opening 25 is formed in the reverse trapezoidal shape, and the silicon oxide layer 22 is exposed through a lower portion of the opening 25. The etching process is performed on the lower portion of the silicon substrate 21 where the first nitride layer is not formed, and the lower portion of the silicon oxide layer 22 is exposed by eliminating a remaining silicon substrate. Thus, the silicon substrate 21 is divided with respect to the opening 25.
However, compared to a highly advanced information processing field which it is required to rapidly write a large amount of data on a recording medium and reproduce the data from the recording medium, it is difficult to improve a writing and reproducing function of the optical information storage apparatus up to a required level of the current technology while the amount of light transmitted through the opening of the probe among transmitted light through an optical fiber is increased in the light throughput rate of the conventional opening.